Sorry this happened to you and your colleague. Just wondering where the tiger comes into it?
I read in Google the term is originally used by British police and it's because the robber acts like a tiger, chooses his prey carefully, observes it for a while before the attack.
It mostly happens in the UK, Ireland and Belgium.
Here all bank robberies have almost disappeared because of the security, hard condemns and above all, banks barely have any cash anymore!